It is well known to those skilled in the art to employ a chromate conversion or passivation coating on the surface of galvanized steel to impart improved corrosion resistance of bare and painted metal, improve adhesion of coatings, and for aesthetic purposes. For example see Corrosion, L. L. Sheir, R. A. Jarman, G. T. Burstein, Eds. (3rd Edition, Butterworth-Heinemann Ltd, Oxford, 1994), vol. 2, chapter 15.3.
Growing concerns exist regarding the toxicity profile of chromium and the pollution effect of chromates discharged into rivers and waterways by such processes. Because of the high solubility and the strongly oxidizing character of hexavalent chromium ions, conventional chromate conversion processes require extensive water treatment procedures to control their discharge. In addition, the disposal of the solid sludge from such waste treatment procedures is a significant problem.
Accordingly, there is a need in the art to provide an effective non-chromate treatment to provide dried in place conversion or passivating coating to inhibit metal surface corrosion and enhance adhesion of paint on or other coatings that may be applied to the surface.
Numerous compositions for providing non-chromate conversion coatings for galvanized steel are known to those skilled in the art.